The puzzles are generated randomly. Therefore, a puzzle can come up multiple times in days or once in 6 months. Also, sometimes a puzzle is very similar with only 1 or 2 differences and just seems to be identical. In any case, the puzzle generator is being rebuilt to generate more and different kinds of puzzles with different and more varied names and places, etc. You can read about it on the Logic-Puzzles.org Discussion board under Changes coming to Logic-Puzzles.org. It is the 1'st post in that section.

I know that they were repeated puzzles since one of them repeated itself within a couple hours so I was able to complete it mainly by memory the second time. But with the new puzzle generator coming in the next month I guess this might not matter.